In a copying machine having a movable optical system for scanning an original to be copied, the original is exposed during feeding of the optical system and the optical system is returned to its home position with a relatively rapid speed. A home position sensor is provided at the home position for stopping the optical system when the home position sensor senses that the optical system is returned to the home position.
However, there can be an error of about ten millimeters or so between the correct home position and the actual stop position of the optical system in conventional copying machine partly because the length of the wire for driving the optical system has been gradually changed and partly because of changes in the sliding friction of a base unit for supporting a lens assembly of the optical system. The change of the stop position of the optical system causes the running speed of the optical system to be unstable even if the optical system comes near a leading position of the picture to be copied when the optical system is started. In order to stabilize the running speed of the optical system at the leading position of the picture in the worst case, there must be a long approach running of the optical system. This long approach prevents decreasing the size of the copying machine.
In addition, stopping the optical system in a correct position requires a first sensor for detecting when the optical system comes near the home position and a second sensor for detecting the correct home position. The signal of these two sensors correctly positions the optical system at its home position.
However, this arrangement requires two sensors. Furthermore, after passing the first sensor, the optical system is moved only the inertia of the fast returning motion and a sufficient braking cannot be obtained. Therefore, the distance between the first sensor and the home position is relatively long. Thus, the distance which does not contribute to the image scanning must be long. Also, as the return speed is not decelerated in the return process, the higher the returning speed, the greater the possibility of error in correctly positioning the system at the stop position.
Furthermore, in attempting to stop the optical system at the correct home position by using a mechanical clutch and/or brake, a strong mechanical shock occurs when the optical system is stopped. In addition, maintenance work for the clutch and brake is required which increases the maintenance cost.